The present invention relates to a laser imaging apparatus which forms an image pattern on a surface to be exposed to light using a beam of non-visible light.
Conventionally, a laser imaging apparatus such as a direct imager of a laser photo plotter has been used for forming a circuit pattern or the like on a printed circuit board or a semiconductor element. In such an imaging apparatus, a substrate carrying a photo-resist is exposed to an image pattern so that the circuit pattern is directly formed thereon.
In such an imaging apparatus, if a gas laser device or a solid laser source which cannot emit an ON-OFF modulated laser beam as a laser source is used, a modulator such as an AOM (acousto-optical modulator) should be used, which complicates the structure of an optical system thereof.
Further, in such an imaging apparatus, when the light source is exchanged, for example, the position/orientation of the exchanged light source should be adjusted with respect to the optical axis of the optical system. If the wavelength of the laser beam is greater than 700 nm (nanometer), or less than 400 nm, since the beam is invisible to the human eyes, a camera or a fluorescent plate should be used to check the position of the beam passing through each component of the optical system. Such a checking procedure is very troublesome.
It is therefore an object of the invention to provide an improved laser imaging apparatus, alignment (positioning) of which can easily be done even though the non-visible laser beam is used for imaging.
For the above object, according to the present invention, there is provided a laser imaging apparatus, that is provided with a light source unit that emits a laser beam including a first beam and a second beam, central axes of the first beam and the second beams substantially coinciding with each other, the first beam including non-visible light, the second beam including visible light, a modulating system that modulates the beam emitted by the light source unit, a deflecting system that deflects the beam modulated by the modulating system, the deflected beam scanning within a predetermined angular range, and an imaging optical system that converges the deflected beam to form a scanning beam spot on a surface to be scanned.
Since the first beam includes the visible light, and the central axes of the first beam and the second beams coincide with each other, the alignment can easily be performed using the visible light.
In a particular case, the first beam is used for forming an image on the surface to be scanned, and the second beam is used for the alignment.
Optionally, the first beam includes light having one or more wavelengths within the non-visible wavelength range, and the second beam includes light having at least one wavelength within the visible wavelength range.
In one configuration, the light source unit may include a first laser source that emits the first beam, a second laser source that emits the second beam, and a beam combining optical system that combines the first beam and second beam such that the central axes of the first beam and the second beam coincide with each other.
In a particular case, one of the first beam and the second beam is emitted from the light source unit as a P-polarized beam and the other of the first beam and the second beam is emitted from the light source unit as an S-polarized beam, and the beam combining optical system includes a polarized beam combiner that receives the P-polarized beam and the S-polarized beam and combines the received beams such that the central axes of the first beam and the second beam coincide with each other.
Optionally, the second laser source may include a laser diode that emits a laser beam having a visible wavelength, and a collimating lens that collimates the laser beam emitted by the laser diode, the collimated beam being the second beam.
In another configuration, the light source unit may include an excitation light source that emits the second beam, which serves as an excitation beam, having a visible wavelength, laser medium that i s excited by the excitation beam to emit the first beam, and a switching system that switches optical paths of the laser beam emitted by the excitation light source such that the laser beam emitted by the excitation light source is emitted from the light source unit or the laser beam emitted by the excitation light source is incident on the laser medium, the first beam being emitted by the laser medium in response to incident of the excitation beam on the laser medium.
Optionally, the laser imaging apparatus may be configured such that only the first beam is directed from the light source unit to the modulating optical system when imaging is performed, and only the second beam is directed from the light source unit to the modulating optical system when alignment is performed.
Optionally, the laser imaging apparatus may include a filtering system provided between the light source unit and the modulating optical system, for selectively transmitting one of the first beam and the second beam.
In this case, the filtering system may include a filtering optical element formed with a first area that transmits only the non-visible light and a second area that transmits only the visible light, the filtering optical element being movable between a first position and a second position, the first area being inserted in an optical path between the light source unit and the modulating optical system when the filtering optical element is located at the first position, the second area being inserted in the optical path between the light source unit and the modulating optical system when the filtering optical element is located at the second position.
If the light source unit includes a first laser source that emits the first beam, a second laser source that emits the second beam, and a beam combining optical system that combines the first beam and second beam such that the central axes of the first beam and the second beam coincide with each other, the first laser source and the second laser source may be selectively actuated so that one of the first beam and the second beam is emitted at a time.
In another configuration, the laser imaging apparatus may include a beam separating optical system that separates the first beam from the second beam so that only the first beam is incident on the surface to be scanned.
In a particular case, the beam separating optical system may be provided on a downstream side of the modulating optical system and on an upstream side of the surface to be scanned.
In a particular example, the beam separating optical system includes a dichroic mirror. Alternatively, a dychroic prism may be employed instead of the dychroic mirror.
Optionally, the modulating optical system may include a reduction optical system that reduces a diameter of a beam incident thereon, a modulator that ON-OFF modulates an incident beam in accordance with an image pattern to be formed on the surface to be scanned, and a collimating lens that collimates the beam modulated by the modulator.
In this case, the modulator may include an acousto-optical modulator.
Optionally, a chromatic aberration of the modulating optical system in respect to the first beam and the second beam is compensated for.
Further optionally, the non-visible light is ultraviolet light.
Still optionally, the light source unit includes a filter that reduces the intensity of the visible light.